This invention relates to a rotary atomizing head particularly suitable for use on a coating machine for coating vehicle bodies or other work pieces.
A rotary atomizing head type coating machine which is advantageous in terms of deposition efficiency and finish quality is generally resorted to for coating vehicle bodies or similar work pieces. A rotary atomizing head to be used on such a coating machine is largely constituted by an assembly of a main body and a hub member.
For instance, described in Japanese Laid-Open Patent Publication No. H9-234393 and its corresponding foreign patents U.S. Pat. No. 5,897,060 and EP0803293A1 is a rotary atomizing head type coating machine employing a rotary atomizing head body, which is provided with a rotational shaft mount portion on the rear side for mounting a rotational shaft of an air motor and which formed in a cylindrical or bell shape in a front portion forward of the rotational shaft mount portion. Further, the rotary atomizing head is provided with a paint spreading surface on the front portion toward marginal paint releasing edges for spreading paint into the form of a thin film, along with a paint reservoir which is formed on a deeper portion than the paint spreading surface. Furthermore, a stepped hub fitting portion is provided between the paint spreading surface and the paint reservoir of the rotary atomizing head body.
On the other hand, the hub member of the rotary atomizing head is fittingly mounted in position within the hub fitting portion in such a way as to cover the front side of the paint reservoir. The hub member is provided with a large number of paint outlet holes in its outer peripheral portions so that paint in the paint reservoir is allowed to flow out onto the paint spreading surface through the paint outlet holes.
An O-ring is fitted either in the inner periphery of the stepped hub fitting portion or on the outer periphery of the hub member, and the hub member is removably retained in the stepped hub fitting portion by resilient force of the O-ring.
At the time of washing the rotary atomizing head for a color change or for other purposes, normally the rotary atomizing head which is mounted on a coating machine is cleaned by the so-called automatic washing operation. Namely, in the case of an automatic washing operation, the rotary atomizing head is put in rotation at a high speed, and a wash fluid such as thinner is supplied from a feed tube to the paint reservoir of the rotary atomizing head thereby to wash away deposited paint from paint contacting portions including the paint reservoir, front and rear surfaces of the hub member, paint outlet holes and paint spreading surface. However, it is usually the case that, after an automatic washing operation, pigment components of the paint still remain and accumulate in or on the paint contacting portions although small in amount. Therefore, if the paint residues solidify in or on the paint contacting portions, the solidified pigments or other components have to be manually removed by the use of a brush or the like.
In the case of the rotary atomizing head according to the above-mentioned Japanese Laid-Open Patent Publication No. H9-234393, a hub member is removably mounted and retained on a stepped hub fitting portion by the use of resilient force of an O-ring. In this case, the O-ring has resiliency in such a degree as to be easily deformable when pushed. Therefore, when the rotary atomizing head is rotated at a high speed, for example, at a speed higher than 40,000 rpm, the inside diameter of the O-ring is increased by the centrifugal force which acts on the O-ring.
On the other hand, the rotary atomizing head and the hub member, which are generally formed of an aluminum alloy, stainless alloy or a hard synthetic resin material. Therefore, even when the rotary atomizing head is put in high speed rotation, deformations of the rotary atomizing head and the hub member under the influence of the centrifugal force are extremely small as compared with the extent of deformation of the O-ring.
This means that, when the rotary atomizing head is put in high speed rotation, the O-ring alone is spread to a larger diameter under the influence of the centrifugal force, losing the ability of holding or retaining the hub member securely in position. As a result of the weakened retention force of the O-ring, there may arise a problem that the hub member starts rattling within the stepped hub fitting portion.
Besides, repeated mounting and dismantling of the rotary atomizing head and the hub member can cause deteriorations in resilient force of the O-ring. If the rotary atomizing head is put in high speed rotation, the O-ring which is in such a deteriorated state in resilient force is no longer capable of securely supporting the rotary atomizing head, and the rotation of the rotary atomizing head becomes unstable. Further, as a result of repeated mounting and dismantling of the rotary atomizing head and the hub member, the O-ring undergoes abrasive wear due to frictional contact with associated parts and needs to be replaced at a high frequency.
Moreover, paint which comes out through the paint outlet holes flows into gap spaces between the stepped hub fitting portion and outer peripheral portions of the hub member during a coating operation, and pigment components of the paint tend to accumulate and solidify there even after conducting an automatic washing operation on the rotary atomizing head even at time of a color change or for other reasons. Therefore, in order to remove the solid contaminants like solidified pigments from the gap spaces, it becomes necessary to dismantle the hub member from the rotary atomizing head body. In such a case, it is often found difficult to dismantle the hub member readily from the main body of the rotary atomizing head because solidified pigments which has stuck into the gap spaces act like wedges. If one try to remove the hub member forcibly by applying strong forces to the rear side of the hub member by the use of a hammer or the like, those portions of the stepped hub fitting portion of the main body and the hub member which are in contacting engagement can be damaged to a serious degree.
On the other hand, the hub member is provided with a large number of paint outlet holes. However, for the purpose of distributing paint from the paint reservoir to the paint spreading surface of the rotary atomizing head, a large number of paint outlet holes of a relatively small diameter are provided along the outer periphery of the hub member. Therefore, as paint passes through the paint outlet holes, pigment components of the paint tend to deposit and accumulate on inner peripheral surfaces of the paint outlet holes, gradually constricting the inside diameter of the paint outlet holes.
As a result of paint deposition and accumulation, the paint outlet holes are varied in diameter. Therefore, paint which flows out onto the paint spreading surface through the paint outlet holes becomes unstable in flow rate, making it difficult to form a thin film of paint uniformly on the paint spreading surface and releasing from the paint releasing edges paint particles of such irregular sizes as would invite degradations in coating quality.
In addition, as the paint outlet holes are constricted in diameter, the paint reservoir is overly filled with paint which is not allowed to flow out smoothly through the paint outlet holes, and the paint begins to overflow into gap spaces around the rotational shaft to give adverse effects on the operation of the air motor.
In this regard, according to the prior art, a narrow rodlike (a needle-like) tool poked into the paint outlet holes one after another to remove accumulated and solidified paint therefrom. This paint removing job is extremely troublesome and time consuming and invites a serious drop in working efficiency.
In view of the foregoing situations, it is an object of the present invention to provide a rotary atomizing head employing a main body and a hub member which can be easily assembled and disassembled.
It is another object of the present invention to provide a rotary atomizing head which can retain a hub member securely within a hub fitting groove even when the rotary atomizing head is put in high speed rotation.
It is still another object of the present invention to provide a rotary atomizing head which permits to remove solidified pigments or other paint residues from paint passages in a facilitated manner.
The present invention is directed to a rotary atomizing head including a main body formed in a bell or tubular shape and having on the rear side a rotational shaft mount portion and on the front side a paint spreading surface extending toward marginal paint releasing edges for spreading paint into the form of a thin film and a paint reservoir provided in a receded deep portion of the main body, and a hub member fitted in an inner peripheral surface of the main body in such a way as to cover up front side of the paint reservoir.
According to the present invention, in order to solve the above-mentioned problems, there is provided a rotary atomizing head which is characterized in that: the main body is provided with a hub fitting groove around the inner peripheral surface between the paint reservoir and the paint spreading surface; the hub member is constituted by a lid portion of a circular disc-like shape having an outside diameter smaller than inside diameter of the inner peripheral surface on the side of the main body, a plural number of leg portions projected axially rearward from the lid portion and having distal end portions adapted to be brought into and out of engagement with the hub fitting groove through resilient deformation, and a plural number of notched grooves each provided between adjacent leg portions; and a plural number of channel-like paint passages are formed by and between the hub fitting groove and the notched grooves when the leg portions of the hub member are fitted in the hub fitting groove, and at the same time an annular paint passage is formed between the inner peripheral surface of the main body and circumferential surface of the lid portion.
With the arrangements just described, by holding the hub member against the main body in such a way as to cover the paint reservoir and then pushing it into the main body, the leg portions of the hub member, which are formed independently of each other, are resiliently deformed radially inward of the inner peripheral surface of the main body and then spread into a larger diameter upon engagement with the hub fitting groove. Consequently, the hub member is securely retained and stopped in the hub fitting groove by the resilient force of the leg portions. When the rotary atomizing head is put in high speed rotation, the respective leg portions of the hub member are spread into a larger diameter under the influence of centrifugal force and strongly pressed against the hub fitting groove to retain the hub member in position with greater retention forces.
Besides, when the hub member is set in the hub fitting groove, channel-like paint passages are formed between the notched grooves and the hub fitting groove, and at the same time the annular paint passage is formed between the lid portion of the hub member and the inner peripheral surface of the main body. Therefore, at the time of a coating operation, paint which has been supplied to the paint reservoir is urged to flow out onto the paint spreading surface through the respective channel-like paint passages and annular paint passage, and sprayed from the paint releasing edges in the form of finely atomized particles toward a work piece and deposited on the latter.
On the other hand, at the time of removing accumulated and solidified paint residues including solidified pigments or other components of paint from the respective channel-like paint passages and the annular paint passage, the hub member can be detached-from the main body simply by pushing a rear surface of the hub member through the rotational shaft mount portion on the front side of the main body. By so doing, the hub member can be easily disengaged from the hub fitting groove even when solidified paint residues are stuck in gap spaces between the respective leg portions and the hub fitting groove, because the leg portions undergo resilient deformation relatively easily in the same manner as they are pushed into the hub fitting groove. In a disassembled state, the channel-like paint passages are split into notched grooves on the side of the hub member and the hub fitting groove on the side of the main body, so that solidified paint residues like pigments can be easily removed from the notched grooves and the hub fitting groove by the use of a brush or the like. In addition, accumulated and solidified paint residues can also be easily removed from other liquid contacting portions including the inner peripheral surface of the main body and a paint receiving surface of the hub member.
According to the present invention, the leg portions and the notched grooves are formed alternately at and along outer periphery of the lid portion, and the channel-like paint passages are formed independently between the notched grooves and the hub fitting groove.
With the arrangements just described, paint which has been supplied to the paint reservoir is uniformly distributed to the annular paint passage through the respective channel-like paint passages.
According to the present invention, the annular paint passage is formed between and entirely around the inner peripheral surface of the main body and the circumferential surface of the lid portion of the hub member.
With the arrangements just described, paint which has been passed through the respective channel-like paint passages is supplied to the paint spreading surface through the annular paint passage.
According to the present invention, the leg portions are spread into a larger diameter in a direction away from the lid portion and toward the distal end portions.
With the arrangements just described, the distal ends of the respective leg portions, which are located in radially outermost positions, can be securely brought into fitting engagement with the hub fitting groove when the hub member is pushed into the main body.
According to the present invention, the hub fitting groove is connected to the inner peripheral surface of the main body through accurately rounded surfaces in front and rear boundary regions.
With the arrangements just described, paint is allowed to flow from the paint reservoir to the paint spreading surface, smoothly riding over the hub fitting groove without scattering around at the edges of the hub fitting groove.
According to the present invention, the annular paint passage is gradually diverged into a larger diameter in a forward direction.
With the arrangements just described, the inner peripheral surface of the main body is diverged in diameter from rear to front side thereof, so that, at the time of mounting the hub member on the main body, the leg portions of the hub member can be gradually bent toward the hub fitting groove through resilient deformation until they fall into engagement with the latter. In addition, paint which has been passed through the respective channel-like paint passages is supplied onto the paint spreading surface through the annular paint passage.
According to the present invention, the annular paint passage is a straight passage having substantially a uniform diameter in an axial direction.
With the arrangements just described, paint which has been passed through the respective channel-like paint passages is similarly supplied onto the paint spreading surface through is the annular paint passage.